Type in the missing numbers.

from left, numbers are : -6 , -2 & 0

-6

Step-by-step explanation:

because the order is -2 so -8 - -2 is -6.

Given that on the graph of y=f(x) the slope at any point (x,y) is always twice the value of x, and f(2)=3, the the function will be given by:
y=kx
where k is the slope. 
but
y=3 when x=2
hence plugging in the above and solving for k we obtain:
3=2k
hence
k=3/2
thus
y=3/2x
thus f(3) will be evaluated as follows:
x=3
plugging in the formula we get:
y=f(3)=3/2(3)=9/2=4.5

y=4.5